1. Field of the Invention
The invention relates to the field of metallization of plastics, especially to a generic method for preparing metal coated plastics, using inherently metal binding poly-diamine-quinone polymers as a binder, for direct immobilization of powdered metals on plastic surfaces forming a metal coated plastic composite, which subsequently can be rendered electrically conducting.
2. Prior Art
In the field of metallization of plastics, many techniques are known to deposit metal atoms onto plastic surfaces, thereby rendering the metal atoms immobile thereon. One technique involves vacuum deposition of metal atoms on plastic surfaces, wherein a thin coating of metal is deposited by condensation on a cool plastic surface in a vacuum. Typically a high vacuum is required, such as 0.1 micron mercury or better. It is also necessary to heat the metal atoms to be deposited to high temperatures.
Another technique involves plasma cathode sputtering of metal atoms onto a glass, plastic, metal or other surfaces, wherein metal atoms are ejected from the surface of a plasma cathode as the result of heavy ion impact and are thereby deposited on a target surface. High temperatures and high vacuum pressure are not required in this technique.
A further technique to deposit metal atoms on a plastic surface involves electroless plating, wherein a metal coating is deposited by immersion of a metal or nonmetal surface in a bath containing a chemical reducing agent. Usually the plastic surface is first sensitized with a strong reducing agent spread over the surface. Then a catalytic amount of a noble metal in a bath is precipitated by reduction onto the sensitized surface.
However, these foregoing techniques, i.e., vacuum deposition, cathode sputtering and electroless plating, have to be tailored to suit specific applications depending upon the metal as well as the plastic chosen. The present invention provides a generic procedure to deposit metal atoms onto plastic surfaces that can be applied to most plastics and nearly all metals and their alloys except alkali and alkaline earth metals chosen without tailoring the process to the particular species involved.
The present invention incorporates, by reference, the use of a particular family of polymers that have very strong inherent affinity towards all metals and their alloys, known as poly-diamine-quinone-polymers (PAQ), which are described in U.S. Pat. Nos. 4,831,107, 4,882,413, and 4,981,946, as a binder to immobilize metal atoms on plastic surfaces.
The PAQ polymers are prepared by condensing various aliphatic and aromatic polyamines with different quinones. Depending upon the characteristics of the ingredients these polymers vary from infusible and intractable ones to those that are tacky, flexible, or brittle. Some can be used as adhesives and coatings. They are also capable of forming fibers from melt as well as solution. Most are curable with heat and chemicals. Before curing they are soluble in lower alcohols such as methanol, ethanol, etc., acetone and DMSO but insoluble in water and ethyl ether. They can be applied by dipping, spraying, brushing and melt coating. Once cured, they are insoluble in solvents and impervious to water, salt water, boiling and autoclaving. They are non-wettable by water. They can displace water from surfaces of metals, including dripping wet rusted steel surfaces.
The present invention provides a generic method of applying metal coatings to plastic surfaces that is applicable to most plastics and nearly all metals and their alloys including gold and platinum and excepting alkali and alkaline earth metals and mercury, using a poly-diamine-quinone polymer as an adhesive binder, which offers distinct advantages over prior techniques of deposition of metal coatings onto plastic surfaces. The present invention is easy to prepare and is more economical to produce in large quantities.
The present invention further provides a method for imparting an electrical conductance very easily to the metal coated plastic product produced by the method of this invention. All of the deposited metals are electrically conducting to varying degrees. Some, like nickel, conduct with practically no resistance, that is, no discernable voltage drop when a potential of 30 volts is applied. Others show greater resistance. However these can be made electrically conducting by known techniques for imparting electrical conductance. One technique of imparting an electrical conductance to a substrate is by immersing substrate into copper-plating baths containing copper sulfate solutions and derivatives thereof.
The present invention is applicable to, but not limited to, applications where the metal coated plastic can be used as a decorative surface and as a stable, abrasion resistant, no flake, polishable surface. Such applications include various plastics used to simulate metal, such as automobile bumper design or the like and decorative jewelry design. Other applications where an electrically conductive surface is required may also employ this invention, for example, the preparation of printed circuit boards.